A bright decorative molded article, which comprises an opaque substrate, a bright decorative layer of indium, tin, tin alloy, or the like formed on the surface thereof, and a transparent resin layer covering the bright decorative layer, has been known. Such molded article develops silver color tone from the material that constitutes a bright decorative layer. Accordingly, molded articles with other color tones have been needed, and those with gold color tone have been needed, especially for luxury automobiles. In general, a thin metal layer with a gold metallic color tone that is used for bright decorative components, such as automobile emblems, is often of yellow chrome plating. This material is characterized by a relatively low level of electric resistance. When such material is used for a front cover of the radar, accordingly, it absorbs a radar beam and does not allow it to be transmitted. This causes deterioration in the performance of the radar, and thus, such material cannot be employed for radar-mounted automobiles under current conditions.
An automatic cruise control system is a technique of measuring a distance from an automobile in front and relative velocity via a sensor mounted in the front part of an automobile, operating the throttle and the brakes based on such information, adequately accelerating or decelerating the automobile, and maintaining an appropriate distance between two automobiles. In recent years, this automatic cruise control system has drawn attention as a core technique of the intelligent transportation system (ITS) that is aimed at easing traffic congestion and reducing traffic accidents. In general, a radio transmitter/receiver unit, such as a millimeter wave radar sensor, has been used as a sensor for the automatic cruise control system.
As shown in FIG. 3, a radar device 100 mounted on an automobile is usually mounted behind a front grille 101. On the front grille 101, an emblem 102 of the manufacturer of the automobile or some other distinctive ornamentation is attached. The radar device emits millimeter waves that are transmitted forward through the front grille and the emblem. Light reflected by an object is returned to the radar device through the front grille and the emblem.
Accordingly, use of materials and coating materials that cause a small radio transmission loss and produce an esthetically pleasing exterior is preferable for parts that are used for the front grille, the emblem, and, in particular, the beam path of the radar device.
As described above, a radio transmitter/receiver unit is generally mounted behind the front grille of an automobile. The front grille, however, is often metal-plated, and it is difficult for highly conductive metal to efficiently transmit radio waves. In addition, the front grille is perforated with ventilation holes for air intake, and the thickness thereof is uneven. If radio waves are allowed to be transmitted through such front grille, accordingly, the rate of radio transmission through the thin portions of the front grille becomes different from that through the thick portions thereof. Thus, it is difficult to obtain accurate radar sensitivity.
JP Patent Publication (Kokai) No. 2000-344032 A discloses a radiator grille cover of an automobile with an improved appearance and inhibited radar wave diffusion, which comprises a transparent flat plate substrate, a black layer provided on part of the back surface thereof, and a colored grille layer, which has approximately the same color as the bars of the radiator grille, provided thereon via indium vapor deposition.
Thus, indium is employed as a metal to be vapor deposited on a radio-transmitting cover. Such metal is not limited to expensive indium, and a variety of metal materials are employed in order to form a metal coating. However, the color tone of such coating is limited to silver.